Vehicle emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations, and then purge the stored vapors during a subsequent engine operation. In an effort to meet stringent federal emissions regulations, emission control systems may need to be intermittently diagnosed for the presence of leaks that could release fuel vapors to the atmosphere.
Hybrid vehicles and other vehicles with inherently low manifold vacuum may perform leak tests while the vehicle is turned off. In some examples, the leak test is based on natural pressure or vacuum that occurs in the fuel tank due to fuel heating or cooling. In some examples, the fuel system may include a vacuum pump configured to draw a vacuum on the fuel tank and evaporative emissions system. In order to increase the accuracy of the leak test, the test may be initiated at a time point following vehicle shut-off, thus allowing for the bulk fuel temperature to stabilize, thus reducing one noise factor that may impact a test result.
However, in order to conserve battery charge to perform the test following a vehicle off condition, the vehicle powertrain control module (PCM) must first be put to sleep, then re-awakened. Waking the PCM at an arbitrary time following the vehicle off condition does not guarantee that the fuel temperature will be stable, or that other conditions for a leak test are met. A vehicle parked in the sun during the day may experience an increase in fuel temperature. Waking the PCM unnecessarily wastes stored battery charge. Executing the leak test at during inopportune conditions may cause false failures that impact the test efficacy. Further, initiating a leak test that will be aborted may involve cycling system valves open and closed, reducing their expected lifespan.
The inventors herein have recognized the above issues and have developed systems and methods to at least partially address them. In one example, a method for a vehicle, comprising: following a vehicle-off event, waking a powertrain control module based on a comparison of an ambient temperature and a bulk fuel temperature; and then initiating an evaporative emissions system leak test. In this way, the evaporative emission leak test may be initiated without waking the powertrain control module arbitrarily. At an arbitrary time point, changes in weather following the vehicle-off event may lead to a failure to meet testing entry conditions, thus reducing the execution rate of the leak test. By waking the powertrain control module and initiating the test based on ambient and bulk fuel temperatures the execution rate can be increased.
In another example, a fuel system for a vehicle, comprising: a powertrain control module comprising a wake input, the wake input configured to wake the powertrain control module responsive to a ratio of a bulk fuel temperature to an ambient air temperature decreasing below a threshold. In this way, the evaporative emission leak test may be initiated when conditions indicate the test is likely to run to completion. In turn, this will decrease the number of false test results and increase the robustness of the test.
In yet another example, an evaporative emissions system for a vehicle, comprising: a fuel tank coupled to a fuel vapor canister; a powertrain control module comprising a wake input; a comparator circuit coupled to the wake input, the comparator circuit configured to output a voltage indicating a ratio of engine coolant temperature to ambient temperature; and wherein the powertrain control module is configured with instructions stored in non-transitory memory that when executed cause the powertrain control module to: sleep following a vehicle-off event; wake responsive to the wake input indicating that the ratio of engine coolant temperature to ambient air temperature has decreased below a threshold; and then initiate an evaporative emissions system leak test; and set a diagnostic code responsive to results of the evaporative emissions system leak test. In this way, battery charge may be conserved by not waking the power train control module arbitrarily. Further, by only initiating the leak test when the test is likely to run to completion, wear and tear on fuel system valves may be reduced, increasing the performance life of the valves.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.